BIM News

Last trends of the AECO sector

Bridge design workflows

Published: 29/06/2018

Country: United Kingdom

The Traditional Approach

Large infrastructure projects these days might consist of a main crossing along with multiple roads and interchanges. During the design pursuit stages, teams need to collaborate across multiple locations and disciplines in order to prepare technical and financial proposals against a field of strong competitors. If successful, the challenges faced during the detailed design, fabrication and construction stages are no less daunting.

For instance, an experienced bridge engineer might look at the proposed highway alignments and establish suitable locations for the substructure and put forward some viable superstructure options that reflect the corresponding span lengths as well as the type of construction that would be appropriate for the given location.

In order to validate these concepts, a number of separate analysis models would be developed, from the very simple continuous beam models to the more complex 3D finite element models, as needed as the design evolves. Often, the results from these analysis models would be imported into various custom spreadsheets to carry out the detailed code checking aspects to meet the requirements of design standards.

Once the design process is sufficiently advanced, the time consuming task of creating the design drawings takes place. In most cases, this task is still very much the domain of the tried and true 2D CAD world. In addition, increasingly so these days, separate and more detailed 3D models need to be created to present the design visualizations to the various stakeholders.

In the above workflow, while some of the software in the individual steps, such as for structural analysis, can be quite powerful and sophisticated, the fundamental limitations have not really evolved in the last couple of decades. In most cases, investigating even relatively minor design variations, such as different number of spans or girders, let alone larger changes such as the type of a superstructure, usually requires one to start all over again. The traditional approach for tackling these challenges is simply no longer sufficient.

Another consideration is that in order to converge to the best solutions (by taking aesthetic, technical and financial issues into account), it would be beneficial to shift the design efforts towards the earlier design stages and allow for the exploration of a wider set of viable options. The corresponding decisions would have a greater impact than the ones made by fine tuning, during the detailed design stage, a prematurely chosen option. Unfortunately, in the traditional workflow, the time and effort required to develop a design leaves little room for such a shift.

A Better Approach – BIM and bridges

In the vertical construction industry, the use of building information modeling (BIM) has already become the norm. Multidisciplinary teams can leverage software tools such as Autodesk’s Revit to tackle the design workflows much more effectively than was the case in the past.

For infrastructure projects, the scale of the projects as well as the inherent geometric complexities of the alignments and structures make for a more challenging proposition.

Autodesk is harnessing the power of cloud computing in order to offer a better way for tackling these type of projects. In doing so, Autodesk is taking a step back and looking at the big picture rather than focusing on individual applications in isolation. In this way, the Autodesk applications will allow users to create and modify different aspects of the central data model in a coordinated way.

Starting with Autodesk’s InfraWorks 360, models for the entire project can be quickly setup that aggregate terrain elevation data, aerial imagery, point clouds, existing infrastructure, and most likely, a number of emerging data sources in the future. This provides teams with a rich contextual setting to explore various options in a collaborative and multidisciplinary manner.

In the case of bridges, experienced bridge engineers and designers can be leading the process by interacting directly with the fully parametric and dynamic components of their models. They can directly apply their past experience and knowledge to create and modify all the relevant parameters that define the components of the bridges: define the type of bridge superstructure, the number of girder lines, the number of piers, the type of foundations; graphically move or skew a pier to reflect the site constraints; adjust any one of the dynamic parameters exposed by the pier, such as the dimension of the columns or the pier cap. Quickly see at a glance, the detailed quantities for the selected pier, superstructure vs substructure or the bridge as a whole, regardless of the geometric complexities. By leveraging Autodesk Inventor’s powerful solid modeling capabilities, users can extend the available libraries by creating their own parametric custom bridge components.

In order to provide users with guidance during the bridge option development stages, the girders of the superstructure can be analyzed and checked with cloud based services that leverage Autodesk Structural Bridge Design (ASBD)’s capabilities. In the case of pre-stressed girders, where possible, a suitable tendon layout, that meets the requirements of the design standards, is identified. Similar capabilities are planned to generate line girder or grillage/finite element models suitable for analyzing and checking steel plate girders and composite box girders to ASHTO LRFD 7 requirements. Moreover, in the future, by leveraging the new Autodesk Forge cloud platform, 3rd party structural analysis software partners will be able to extract their own analytical representations from the Autodesk BIM model and provide more advanced or specialized capabilities.

While the modeling of the bridges may appear to be deceptively simple, by virtue of the fact that the underlying components are based on accurate parametric geometry, they can readily be progressed towards detailed design without having to be recreated. In fact, a full model can be quickly opened up in Autodesk’s Civil3D or Revit software where the rest of the team of designers and technicians can complete the detailed modeling. In order to accommodate the complex geometric requirements of civil structures in general and bridges in particular, a number of enhancements are being developed in Revit itself. These will allow users to model reinforcing steel and to properly dimension structural components that have arbitrarily complex geometric layouts. Further enhancements are also being made to handle an increased level of detail for steel structures, including connections. With all these enhancements, creating a live model of the project becomes feasible.

With the help of such detailed and accurate models, construction drawings can be effectively created and the models themselves can be leveraged in different phases of the project’s lifecycle. While much more can be said in the so called BIM to Field domain, just the ability to export rebar schedules and structural steel in a coordinated way to the fabrication and construction stages presents many advantages.

This overall BIM approach will allow teams to make small or big changes at the concept or detailed design stages without having to rework or start all over again. By making sure that the various Autodesk solutions work harmoniously together and with the central data, the burden and strain of attempting to keep data in sync becomes an artifact of the past. By championing the use of open standards, such as IFC, the Autodesk solutions will offer even greater possibilities.